This invention relates to an electrophotographic photoconductive material and, particularly, to a novel electrophotographic photoconductive material having a photosensitive layer containing an azo pigment. More particularly, it relates to a highly durable electrophotographic photoconductive material excellent in sensitivity and suitable for repeated use.
There have, heretofore, been widely known electrophotographic photoconductive materials having photosensitive layers containing as major constituent inorganic photoconductive substances such as selenium, zinc oxide, cadmium sulfide, and the like. These photoconductive materials, however, are not entirely satisfactory in sensitivity, thermal stability, moisture resistance, and durability. Especially, the toxicity of selenium and cadmium sulfide imposes some restriction on their manufacture and handling.
In recent years, electrophotographic photoconductive materials having a photosensitive layer containing as major constituent an organic photoconductive compound have attracted much attention because of the ease of their manufacture and other advantages including thermal stability which is generally superior to that of the selenium photoconductor. A well-known organic photoconductive compound is poly-N-vinylcarbazole. However, a photoconductive material having a photosensitive layer containing as major constituent a charge transfer complex formed from poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone is not entirely satisfactory in sensitivity and durability.
There are also known photoconductive materials of the functionally separated type such as a laminated type and a dispersion type, in which the carrier generating function and the carrier transfer function are respectively borne by different substances. Such a type of photoconductive material has advantages in that the materials can be selected from a wide range to facilitate the preparation of photoconductive materials having any of the intended characteristics such as charge characteristics, sensitivity, durability, and the like.
Various substances have been proposed to be useful for the generation or transfer of the carrier. For instance, there is actually in use an electrophotographic photoconductive material having a photosensitive layer comprising a combination of a carrier generating layer containing amorphous selenium and a carrier transfer layer containing poly-N-vinylcarbazole as major constituent. The carrier generating layer comprising amorphous selenium, however, has a drawback of unsatisfactory durability.
It has also been proposed to use organic dyes or pigments as carrier generating substance. For instance, photoconductive materials having photosensitive layers containing, for example, monoazo or bisazo pigments are described in Japanese Patent Publication No. 30,513/73, Japanese Patent Application "Kokai" (Laid-open) Nos. 4,241/77 and 46,558/79, and Japanese Patent Publication No. 11,945/81. These azo pigments, however, are not entirely satisfactory in photo characteristics such as sensitivity, residual potential, or stability in repeated use. When such a pigment is used as carrier generating substance, the carrier transfer substance should be selected from a limited range. Thus, the fact is that there is no carrier generating substance which satisfactorily meets a wide variety of requirements of the electrophotographic process.